I use WD 40 on all my guns, I ran a test on a cap and ball pistol I loaded all 6 cylinders put caps on and soaked it with WD 40 spraying cylinder down barrel let it soak for over a week, then tested it, guess what all 6
went off no delay.
When black powder hunting I run a patchwith WD40 on it down my loaded barrel to prevent rust.

James M